A Modest Proposal for Naming a Hypothetical Distant Planet in the Solar System

The need to choose appropriate and meaningful names for the objects of scientific inquiry, in the spirit of Michael Faraday and, on a different level, of the ancient Chinese doctrine of rectification of names (正名, Zhèngmíng), is illustrated here in the case of the so-called Planet Nine. Since before the discovery of Neptune, the fascinating hypothesis of the possible existence of a new, distant planet in the solar system, yet to be discovered, has regularly surfaced in the pages of astronomy journals in various guises. Its most recent incarnations have been tentatively given names such as Planet X, Planet Y, and, most famously, Planet Nine. Such labels are unsatisfactory because they reveal no significant physical or orbital properties of the object which they are attributed to. I propose here the name Telisto, from the ancient Greek word τήλɩστoς for ‘farthest, most remote’ which captures a feature common to all versions of this scenario that seems destined to remain at the forefront of astronomical research for a long time to come: its supposedly great heliocentric distance, estimated at several hundred astronomical units. By exploring the history of astronomy, I also respond to some criticisms that might be leveled at this proposal. Among other things, I also draw a comparison with the naming of the so-called axions, which are hypothetical elementary particles proposed almost fifty years ago and which continue to be an active object of research.